Lecture Tutorials. For Introductory Astronomy Solar System. By: Jessica Smay Karen Kortz

Transcription

1 Lecture Tutorials For Introductory Astronomy Solar System By: Jessica Smay Karen Kortz

2 Table of Contents Earth and the Moon 1. Earth s Tectonic Plate Boundaries Earth s Surface Features Auroras The Moon s Crater History The Moon s Surface: Order of Events.. 7 Planets and other Space Objects 6. Planetary Positions Terrestrial Planets Vs Jovian Planets Rock Types on Other Planets Planet Surface Features Volcanoes on Other Planets Mars Climate Change Other Moons Surface Processes Jovian Planets Space Objects Asteroid Impacts Pluto Missions DRAFT EDITION, 2009 LECTURE-TUTORIALS FOR INTRODUCTORY GEOSCIENCE i

3 Earth s Tectonic Plate Boundaries Part 1: The Plate Boundaries Read the brief descriptions about what happens at each of the plate boundaries. 1) Draw arrows on each diagram (side view and overhead view) indicating the direction of plate movement. 2) Circle the landforms listed in the final column that occur at each plate boundary 3) Label the landforms in each diagram (side view and overhead view). What Happens Diagram of Plate Boundary (the heavy line is the plate boundary) Landforms Divergent Two tectonic plates move apart and magma erupts to form a high area between the plates. (side view) Tectonic plate Tectonic plate Ocean ridge Volcanoes Subduction trench (overhead view) Convergent Two tectonic plates move toward each other, and one plate is pushed under the other plate. (side view) Tectonic plate Tectonic plate Ocean ridge Volcanoes Subduction trench (overhead view) Part 2: Finding Plate Tectonics on Other Planets 4) Circle one or two features that you would use to determine whether other distant planets have plate tectonics. Explain why you chose which one(s) you did. Divergent ridges Volcanoes Subduction trench 1

4 Earth s Surface Features The features found on the surface of a planet or moon gives clues about that planet or moon. For example, it is impossible to see wind, but it creates sand dunes. Interpretation of Earth s features is the first step to interpreting features on other planets. Part 1: Features 1) How did these sand dunes form? 2) Would it be possible for these sand dunes to form on a planet: a) with no atmosphere? Yes or No b) with no liquid water? Yes or No Explain. 3) How did this impact crater form? 4) Would it be possible for an impact crater to form on a planet: a) with an atmosphere? Yes or No b) with a hot, molten interior? Yes or No Explain. 5) How did these stream beds form? 6) Would it be possible for stream beds to form on a planet: a) with no hot, molten interior? Yes or No b) with no liquid? Yes or No Explain. 2

5 Earth s Surface Features 7) How did this volcano and lava flows form? 8) Would it be possible for volcanoes and lava flows to form on a planet: a) with no liquid water? Yes or No b) with no hot, molten interior? Yes or No c) with no atmosphere? Yes or No Explain. 9) How did this divergent ridge form? 10) Would it be possible for this divergent ridge to form on a planet: a) with no hot, molten interior? Yes or No b) with no liquid water? Yes or No Explain. 11) Two students are discussing their answer to the previous question. Student 1: A divergent ridge is formed by two plates moving apart because of plate tectonics. You need a hot, molten interior in order to form the convection currents that cause plate tectonics. Student 2: But I thought divergent ridges only form in the middle of oceans. Without an ocean, the plates can t move apart, so you need both a hot, molten interior and liquid water. Do you agree or disagree with one or both students? Explain your reasoning. 12) Imagine a new planet is discovered that has sand dunes, impact craters, stream beds, volcanoes and plate tectonics. Circle what we can figure out about that planet: Explain. It has an atmosphere It has liquid It has a hot molten interior 3

6 Auroras Earth has auroras (Northern and Southern lights) because it has a hot interior that rotates forming a magnetic field. This magnetic field forces the solar wind toward the poles where it interacts with our atmosphere. Here we will consider if the Moon has auroras. The Moon formed 0.1 billion years after Earth formed when a large object hit Earth and material splattered into space. The lighter material (gas) drifted away and the heavy, rocky material began to collect and eventually form the Moon. 1) How did the way the Moon formed affect the amount of light materials (gasses) that might have created an atmosphere on the Moon? The amount of gases on the Moon was (circle one) increased or decreased Explain. The Moon s diameter is ¼ the size of Earth s diameter. The Moons mass is 6% Earth s mass. Moon Earth 2) How does the relative size and mass of the Moon affect its ability to retain an atmosphere? a) The Moon s size and mass is relatively (circle one) large or small b) The Moon s gravity is relatively (circle one) strong or weak c) Therefore, its ability to retain an atmosphere is (circle one) good or poor 3) Based on your answers to 1 and 2c, does the Moon have an atmosphere? The relatively small size of the Moon also means that it has cooled and no longer has a hot, molten interior. 4) Does the Moon currently have a magnetic field? Explain. 5) Knowing the cause of Earth s auroras, explain two reasons why the Moon does not have auroras. 6) The Moon s diameter is 3,500 km diameter, Mercury s diameter is 4,900 km, and Earth s diameter is 12,800 km. Suppose there is a mission planned to go to Mercury. Because Mercury is closer to the sun, they want to study its auroras. Would you fund this mission? Explain. 4

7 The Moon s Crater History Part 1: Data Collection Moon samples have shown the highlands formed 4.5 billion years ago (bya) and the mare basalt lava flows formed between 3.8 and 3.1 bya. During this time, objects have impacted the surface forming craters. You will determine how the impact rate has changed. The smoother surface is mare basalt and the rougher surface is highlands. In this photo, the area covered by the mare basalt is essentially the same as the area covered by the highlands. 1) Estimate the number of craters on each surface that are larger than this dot: Do not take more than 1 minute to count! Mare basalt Highlands Part 2: Interpretation of the Data To determine if the impact rate changed over time, we will look at two different periods of time. We will look at the Early Period recorded in highland rocks formed 4.5 bya, and the Late Period recorded in mare basalt rocks formed 3.8 bya. 2) On the timeline, label the arrows as highlands form and basalt erupts. Early Period Late Period 4.5 bya 3.8 bya present 3) How long was the Early Period? by How long was the Late Period? by 4) If the rate (number of craters per year) stayed constant, which of these periods would you expect to have recorded the most impact craters total? (circle one) Early Period Late Period To simplify the next discussion, for the rest of the exercise we will use a count of 22 impacts for the highlands and 8 impacts for the mare basalt. 5

8 The Moon s Crater History 22 impact craters formed on the highlands throughout the whole 4.5 by. If the mare basalt had not erased the surface, it would also have collected 22 impact craters. However the basalt did erase the surface 3.8 bya, and since then the mare basalt only collected 8 impact craters. 5) With 22 impacts total, and 8 impacts since the mare basalt, write in the diagram below how many craters likely formed on the surface before it was erased. impacts 22 impacts 8 impacts 4.5 bya 3.8 bya mare basalt eraser present 6) Compare your results to your answer to Question #4. Did the rate stay constant? To determine an average impact rate in the Late Period, the number of impacts (Q 5) is divided by the time (Q 3). 8 impacts 3.8 by = 2.1 impacts/by This means that since 3.8 bya, during each billion years roughly 2 new craters formed on the surface of the mare basalt in the photograph. 7) Using the same technique, determine the impact rate during the Early Period. Earlier you determined the number of impacts during that time (Q 5), as well as the length of time (Q 3). Part 3: Discussion 8) The number of impacts per billion years has (circle one) increased decreased 9) Circle the graph that best represents the impact rate (number of impacts over time). Number of impacts Number of impacts Number of impacts Number of impacts 4.5 bya present time 4.5 bya present time 4.5 bya present time 4.5 bya present time 10) Why were there so many meteor impacts soon after the formation of the Moon, but later the number of meteor impacts per billion years is so small? 11) Estimate the number of craters that will form in the area shown on the photograph in the next billion years. 6

9 The Moon s Surface: Order of Events Part 1: Crater Relative Ages The following are craters and basalt on the Moon s surface. In each scenario determine the order of events and label them with the first event as 1, the second as 2 and so on until you have labeled all of the events. An event may be crater formation or mare basalt eruption. A crater with rays is fairly young, but there may be younger craters without rays. Basalt is shown as a filled-in gray area. Examples: 1 2 Crater Crater Ray 2 1 Basalt filled crater Crater 2 1 1) (2 events) 2) (2 events) 3) (3 events) Basalt filled crater Crater on basalt 4) (4 events including basalt) 7

10 The Moon s Surface: Order of Events The diagram below shows a portion of the surface of the Moon. 5) Use the same techniques to determine the relative ages of the events. The creation of four craters named Copernicus, Sinus Iridum, Mare Imbrium, Archimedes, and the flooding of the basalt. Sinus Iridum Crater Mare Imbrium Archimedes Copernicus Oldest (first) Youngest (last) 8

11 Planetary Positions Part 1: View from above Below is a representation of the Sun, and the orbits of Earth, Venus and Mars (not to scale!). We will look at the positions of Venus and Mars one planet closer to the Sun, and one farther. 1) For each location of Venus and Mars, shade in the side of the planet not lit by the Sun, and label the planet good view or can t see for an observer on Earth when Earth is in its labeled position. Mars opposition Earth Venus inferior conjunction Sun Venus superior conjunction Mars conjunction Write your answers to the following questions on the diagram. 2) Next to Mars conjunction, explain why it is impossible for astronomers on Earth to view Mars. 3) Next to Venus in inferior conjunction, explain why it is impossible to view Venus 4) Draw and label Venus s best position(s) for a viewer on Earth to see it and explain why. 5) Next to Mars opposition, explain two reasons why this is the best time to view Mars. 9

12 Planetary Positions 6) When Mars is at opposition, the view from Earth will show Mars to be in what phase? (shade in the circle) 7) What time(s) of night would be the best time to view Mars in opposition? (it may help to draw a person on Earth in the diagram) Explain. just before sunrise midnight just after sunset 8) If you were standing on Mars at this time (opposition), could you see Earth? yes no 9) For which other planets would these answers be the same as your answers for Mars? Mercury Venus Jupiter Saturn Uranus Neptune 10) Two students are discussing how Mars looks from Earth at opposition. Student 1: As seen in the diagram, only half of Mars is lit by the Sun, so I drew it half lit and half in shade. Student 2: The view you drew is from directly above Mars. Our view from Earth is different. We have to look directly away from the Sun to see Mars at opposition, so we see only the lit side. Do you agree or disagree with one or both students? Explain your reasoning for each. 11) When Venus is in inferior conjunction, the view from Earth will show Venus to be in what phase? (shade in the circle) 12) If you were standing on Venus at this time, could you see Earth? yes no 13) What time(s) of night would be the best time to view Venus? (it may help to draw a person on Earth in the diagram) Explain. just before sunrise midnight just after sunset 14) For which other planets would these answers be the same as your answers for Venus? Mercury Mars Jupiter Saturn Uranus Neptune 10

13 Terrestrial Planets Vs Jovian Planets Part 1: Density vs Diameter The diameter and density for the planets and Pluto have been plotted on a bar graph. Listed below each planet is the composition. 5,400 5,200 5, , ,000 Diameter kilometers Density kg/m 3 3,900 51,000 50,000 2,000 1,300 1,300 1,600 5,000 12,000 13,000 7,000 2,000 Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto Rock Rock Rock Rock H and He gas H and He gas H and He gas, methane H and He gas, methane 1) Divide the planets (not Pluto) into two groups based on the density, diameter and composition. Group 1 Group 2 Diameter: small or large small or large Density: high or low high or low Composition: rock or gasses rock or gasses 700 Methane ice, rock Planet Names: 2) Label the group of larger, low density gassy planets Jovian planets and the group of smaller, high density, rocky planets Terrestrial planets. 3) Does Pluto fit exactly with either of the groups? Explain. 11

14 Rock Types on Other Planets On Earth there are igneous, sedimentary, and metamorphic rocks. Understanding the way they formed allows us to determine whether or not we are likely to find them on other planets. 1) Match the rock type with the correct statement describing its formation. Found where the atmosphere or liquid water causes erosion and movement of rock pieces Found mostly near convergent tectonic plate boundaries where the temperature and pressure can be very high. Found in places where the interior is so hot that rock melts On the Moon, the first rocks to form when it was molten were the outermost low-density rocks that cooled to form the highlands. Then molten rock filled in the lower areas and cooled. This rock is called the mare basalt. 2) Based on these descriptions, of what type of rock are the highlands and mare basalt composed? Highlands: igneous sedimentary metamorphic Mare basalt: igneous sedimentary metamorphic 3) Where in our solar system might we find igneous rocks? Explain your choice based on what factors are necessary for an igneous rock to form. 4) Where in our solar system might we find sedimentary rocks? Explain your choice based on what factors are necessary for a sedimentary rock to form. 5) Where in our solar system might we find metamorphic rocks? Explain your choice based on what factors are necessary for a metamorphic rock to form. 6) What is the most common rock type in the Solar System? 12

15 Planet Surface Features Part 1: Observations and processes On the next pages are images of four different Earth-like planets (Mercury, Venus, Earth, and Mars). All the images are of the solid, rocky surface. 1) Examine these images and identify the type of surface feature shown: sand dunes, impact crater, lava flows, divergent ridge. 2) For each, write down the process that created the feature in the image: wind, meteor impact, flowing water, hot molten interior, plate tectonics. Planet 1 Earth Planet 1 (a) Feature: Divergent Ridge Process: Tectonic plates moving apart Planet 1 (b) Feature: Process: Planet 1 (c) Feature: Process: Planet 2 Is this planet large enough to retain an atmosphere? Is this planet large enough to have a current hot interior? Planet 2 (a) Feature: Process: Is this planet large enough to retain an atmosphere? Is this planet large enough to have a current hot interior? 13

16 Planet Surface Features Planet 3 Planet 3 (a) Feature: dust streak Process: Planet 3 (b) Feature: volcano and lava flows Process: Is this planet large enough to retain an atmosphere? Is this planet large enough to have a current hot interior? Planet 4 Planet 4 (a) Feature: Process: Planet 4 (c) Feature: Process: Planet 4 (b) Feature: Process: Feature: impact craters Process: Is this planet large enough to retain an atmosphere? Is this planet large enough to have a current hot interior? Notice that the presence of some impact craters indicates that this feature has not been modified for millions of years! 14

17 Planet Surface Features Part 2: Hypotheses In general, larger terrestrial planets have more internal heat and smaller planets have lost their internal heat (medium planets had internal heat for a while, but they are cool now). Also, larger and medium planets retain an atmosphere, while smaller planets do not have enough gravity to retain an atmosphere. The table below shows the diameters of four planets in our solar system. Note that Planet 1 is Earth. Planet Mercury Venus Earth Mars Diameter (km) ,104 12, ) Based on the size of each planet, determine which images are from which planet. Go back and label Planets 2, 3 and 4 with the correct name of the terrestrial planet. 4) What is the primary surface feature on small terrestrial planets? 5) Mars is an intermediate-sized planet. How does it have characteristics of both large and small planets? 6) If an Earth-sized planet were discovered just beyond the orbit of Mars, what surface features should we expect to find when we send a spacecraft to observe the surface? 7) Three students are discussing their answer to the previous question. Student 1: Because the planet is the same size of the Earth, it should have the same surface features as the Earth, like volcanoes, dunes, and stream beds. Student 2: Except the planet is farther from the Sun, so there it should be colder. It can t have any of those features because it would be too cold, so it would have craters. Student 3: Well, maybe the outside of the planet is too cold for stream beds to form, but the inside of the planet will still be hot, so there will be volcanoes. And it is big like the Earth, so there is lots of gravity, so there will be dunes. With which student do you agree? Explain your reasoning. 15

18 Volcanoes on Other Planets Part 1: Observing Volcano Distribution When a scientist makes a discovery, it helps to have as many different sources as possible confirm that discovery. Here we will look at two ways to determine the types of volcanoes on other planets. 1) Examine the maps of volcanoes on Mars, Venus, and Earth. Take 1 minute to describe what kinds of patterns (or lack of patterns) you see in the location of volcanoes on each planet. Volcanoes on Venus (triangles) Volcanoes on Earth (dots) Volcanoes on Mars (stars) Part 2: Analysis Two locations at which volcanoes form are at randomly-distributed hotspots or lined up along tectonic plate boundaries. A single planet might have both types of volcanoes. 2) Why do the volcanoes on Earth form where they do? hot spots plate tectonics Explain how your answer is related to your observations about the maps. 3) Why do the volcanoes on Venus form where they do? hot spots plate tectonics Explain how your answer is related to your observations about the maps. 4) Why did the volcanoes on Mars form where they did? hot spots plate tectonics Explain how your answer is related to your observations about the maps. 5) Which planet(s) has/have plate tectonics? Venus Earth Mars 16

19 Volcanoes on Other Planets Another way to determine the cause of volcanoes on other planets is to compare the two types of volcanoes on Earth with volcanoes on other planets. Plate tectonic volcanoes on land (e.g. Mount St. Helens) have steep slopes, and hot spot volcanoes (e.g. Hawaii) have gentle slopes. 6) Look at the profile of volcanoes on Earth drawn to scale. Label the two volcanoes as hot spot volcano or plate tectonic volcano. 120,000 m 20,000 m Below is an example of a volcano on Mars. We can use the elevations determined by a satellite to create a profile like the ones of Earth shown above. 20,000 m 40,000 m 60,000 m 0 m 600,000 m 7) Knowing that this volcano on Mars is 21,229 meters tall, roughly sketch the profile of this volcano on the graph above. 17

20 Volcanoes on Other Planets 8) Based on the profiles, is the volcano on Mars a hot spot volcano or a plate tectonic volcano? Explain. You used two methods to determine the type of volcanoes found on Mars: the distribution of volcanoes to determine the likely source of volcanism, and the profile of an individual volcano. 9) Do your two data sets agree? If they do not agree, what might cause the difference? 10) Why is it helpful for a scientist to have two or more different data sets when giving evidence to support a discovery? 18

21 Mars Climate Change Part 1: Surface Features In order to understand the climate of Mars, we need to understand how the geologic history, atmosphere, and climate of Mars are all related. This is a photo of Olympus Mons, a volcano on Mars. 1) How can you tell there has not been an eruption for a long period of time? 2) Based on this photo, does Mars currently have a hot, molten interior? Yes No 3) Did Mars have a hot, molten interior in the past? Yes No Olympus Mons This is a photo of some dried stream beds on Mars. 4) How can you tell that this river system on Mars has not had flowing water for millions of years? Part 2: Causes of Interior Heat vs Surface Heat It is very important to understand the causes of a hot interior compared to the causes of a hot surface. 5) Which does the Sun heat? the interior (core) of a planet the surface of a planet 6) Does the distance of a planet from the Sun affect the heat of the interior? Why or why not? 7) Why are Earth s and Venus interiors still hot, but the interior of Mars and Mercury have cooled, even though they all formed at the same time 4.6 bya and Mercury is the closest planet to the Sun? 19

22 Mars Climate Change The temperature of the interior is related to planet size. Next we need to determine what affects the temperature of the surface. 8) Look at the map of volcanoes on Mars. Is it likely that the heat from the lava from these volcanoes was enough to heat the surface and melt all the water that formed the rivers on Mars? Yes No Volcanoes on Mars If lava did not heat the whole surface, something else did. When Mars had a hot molten interior, volcanoes also emitted greenhouse gasses (e.g. CO 2 ) into the atmosphere. 9) Most of the volcanism on Mars stopped 3 billion years ago when the interior cooled. This means Mars used to have (more/less) greenhouse gasses. As a result the atmosphere used to be (thicker/thinner) than now, and therefore the surface temperature, used to be (greater/less) than now. 10) Use the following terms to explain the causes and effects of the listed items below. (liquid water on surface, active volcanoes, CO 2 in the atmosphere, warmer climate) A hot molten interior caused: Volcanoes erupted causing: Greenhouse gasses in the atmosphere caused: A warmer atmosphere caused: Part 3: Predicting Surface Features The warm interior meant volcanoes erupted greenhouse gasses which kept the surface of Mars warm enough for there to be liquid water. Now that the interior of Mars is cool and solid, there is less greenhouse gas in the atmosphere so the whole surface is cooler. 11) Circle the features that were forming on the surface of Mars billions of years ago. volcanoes sand dunes rivers lakes craters 12) Circle the features that are forming on the surface of Mars right now. volcanoes sand dunes rivers lakes craters 13) How was early Mars different than Mars today? (Why is your answer to question 11 different than your answer to question 12?) 20

23 Other Moon s Surface Features The moons of planets in our solar system have features that form the same way as features on terrestrial planets. Two other parameters can affect the surface features on other moons. 1. Strong tides can cause a hot, molten interior, even on a small moon. 2. Liquids other than water can occur on moons that are too cold for liquid water. 1) What features would you expect on the surface of each moon? You may repeat answers. Choose from: many craters few craters stream beds divergent ridges volcanoes a. Typical small moon: An asteroid captured by the gravitational field of a planet. Not large enough to be a spherical moon. b. Typical large moon: A geologically inactive moon that does not experience strong tidal forces. This moon is large enough to have enough gravity to be a spherical moon. c. Io: Orbits very near Jupiter (a Jovian planet) and is strongly affected by the tidal forces of Jupiter. The tidal forces cause heat that escapes at the surface. d. Europa: Orbits close to Jupiter, so that there are strong tidal forces. Cracks in the surface ice can be seen where liquid water has recently welled up. Liquid water beneath the ice may be heated by volcanic vents. e. Titan: One of Saturn s moons. It is too cold for there to be liquid water on the surface, but it is the correct temperature for liquid methane to exist. This liquid methane evaporates and creates cloud cover over the surface. 2) Write the name from the description above next to each of the images of moons below. streams atmosphere Ice plate tectonics few craters volcanoes small large 21

24 Other Moon s Surface Features 3) Why does Io have very few craters? 4) Why does Europa have very few craters? 5) Why does Titan have very few craters? You have been commissioned by NASA to find life elsewhere in the solar system. Both Titan and Europa have important characteristics when searching for life. a) liquid, b) the right composition molecular building blocks c) an energy source (sunlight or internal heat) 6) Which of these two moons would you explore first, and why? 22

25 Part 1: Wind Bands The rotation of a planet can cause winds to blow in certain directions at different latitudes. A simplified version of Earth s wind pattern is shown in the diagram. Jovian Planets 90 o Easterlies 60 o Westerlies 30 o Earth 1) When you see the weather report, think about which direction the winds generally blow across the United States. Use the diagram to the right to determine where you live. 0 o 30 o N 30 o 60 o N 60 o 90 o N The Jovian Planets rotate faster than Earth (even though they are larger! Easterlies 0 o N Easterlies 2) Based on this information, does Jupiter have a well defined wind pattern with obvious bands of wind, or no clear wind pattern? Explain your decision. 30 o Westerlies 60 o Easterlies 90 o Part 2: Auroras Any planet might have auroras if it has a magnetic field and an atmosphere. Earth has a magnetic field caused by a rotating molten iron core. The hydrogen in the core of Jupiter acts as a liquid metal and also creates a magnetic field. Earth 3) Based on this information, does Jupiter have auroras at the North and South poles? Explain your decision. 4) Consider the following discussion between these students. Student 1: The interior of a Jovian planet is squished very dense and the hydrogen acts like a liquid metal creating a magnetic field. However, I do not think there is an atmosphere, so there cannot be any auroras. Student 2: Jovian planets do have atmospheres. I heard they are made completely of gasses, so a spacecraft could fly in one end and out the other. Since they are composed only of a gas atmosphere, there cannot be a magnetic field, so there are no auroras. Student 3: The interiors of the Jovian planets are so squished they act like liquid metals, but the outer gasses are like an atmosphere. I think Jovian planets probably do have auroras. Do you agree or disagree with these students? Explain your reasoning. 23

26 Jovian Planets Part 3: Jovian Planet Features With bands of wind traveling in opposite directions, storms sometimes form in the gasses of the Jovian planets. 5) On the photo on the right, draw arrows in the direction the wind at the top and bottom of the photo might be blowing. One feature found on all Jovian Planets but not on terrestrial planets is the rings. Rings are thought to form from the debris from a collision of moons orbiting the planet. This debris slowly falls out of orbit, so for most Jovian planets special techniques are needed to detect what is left of previously formed rings. 6) Label the planets below. Jupiter: fastest rotation, obvious wind banding Uranus: almost no visible wind banding Saturn: moons collided millions of years ago Neptune: almost no visible wind banding, some storms visible 7) For each arrow, identify the feature and write down the processes that created it. 24

27 Space Objects Asteroids, comets and meteoroids are lumps of material in our solar system. They are different from each other in size, location of formation and type of orbit around the Sun. Meteoroid: Small objects ( 100 meters) composed of rock and/or iron that orbit the Sun in the inner solar system where it was too hot during formation for ices to form. Asteroids: Large objects ( 100 meters) composed of rock that generally orbit the Sun between Mars and Jupiter. Asteroids are too small to be planets, but they are much larger than meteoroids. Kuiper Belt Objects: (KBO s) Large objects composed of rock and ice that orbit the Sun from Pluto s orbit at 40 AU out to 500 AU. KBO s are generally too small to be planets (few over 2,000 km). Comets: When the orbit of a KBO is so elliptical that it comes into the inner solar system, we call it a comet. When it is near the Sun, the solar wind hits the ice and causes a coma and tail to form around the nucleus. 1) Based on their composition, explain which objects formed in the inner solar system and which objects formed in the outer solar system. 2) Explain if each of these objects is orbiting the Sun, a planet or some other object. Meteoroid Asteroid KBO Comet 3) Consider the following discussion between these students. Student 1: These objects do not orbit planets, they orbit the Sun. If they were sitting still, their gravitational attraction to the Sun would pull them in. Student 2: I agree that these objects do not orbit planets. If they did, they would be called moons. However, I think these objects are not orbiting anything. They are floating in the space between the planets. Do you agree or disagree with all or part of these statements? Explain your reasoning. 25

28 Space Objects 4) Label each image as an meteoroid, asteroid, KBO, or comet. a) b) c) d) has a coma and tail rock rock and ice visible for 1 second 5) This is a diagram of the Solar System. Draw and label one example orbit for a meteoroid, an asteroid, a KBO and a comet. Pluto Neptune Uranus Saturn Jupiter Mars 26

29 Asteroid Impacts One estimate indicates there are around 10,000 asteroids larger than 1 km. There is usually over 1 million km between asteroids. Asteroids are so few and far between, that you could stand on one asteroid, and you would need a telescope to see the nearest neighbor asteroid. 1) To the best of your ability, draw a scale model of two asteroids at an average distance apart. 2) If a 1 km diameter asteroid is represented with a 1 mm grain of sand how far away would the next asteroid be if in real life it is 1,000,000 km away? a) 100 mm (4 inches) b) 10,000 mm (10 yards) c) 1,000,000 mm (1,000 yards) 3) Compare this result with your drawing and explain any difficulties you might have with accurately drawing two asteroids to scale. 4) The inner solar system is often drawn as shown. However, if Earth was the size indicated, the Sun should be the size of a baseball 30 feet away. What would you need to change to make this an accurate representation of the asteroid belt? 5) From Earth, we have sent many spacecraft to other planets. For which planets do our spacecraft travel through the asteroid belt? (circle all that apply) Mercury Venus Mars Jupiter Saturn Uranus Neptune None of these 6) For which planets is it necessary for spacecraft to take extra precautions (e.g. guided flight path) to avoid the asteroids in the asteroid belt? (circle all that apply) Mercury Venus Mars Jupiter Saturn Uranus Neptune None of these 7) Consider the following discussion between these students. Student 1: I think we need to avoid the asteroid belt for the Jovian planets because they are the ones on the other side of the asteroid belt. Student 2: Because the asteroids are so few and far apart in the asteroid belt, we do not need to worry about avoiding the asteroid belt for any of the planets. If we need to, we can fly straight through! Do you agree or disagree with all or part of these statements? Explain your reasoning. 27

30 Pluto Part 1: Comparison to Terrestrial and Jovian Planets You are on a committee to determine whether or not to classify Pluto as a planet. Some facts about Pluto: - diameter is 2,320 km (large enough to be round) - orbit averages 40 AU ( which is in the Kuiper Belt) - composed of rock and ice. Pluto 1) What are three characteristics the Terrestrial planets have in common? Consider density, diameter (size), gasses in the atmosphere, composition, orbit size, rings. 2) What are three characteristics the Jovian planets have in common? Consider density, diameter (size), gasses in the atmosphere, composition, orbit size, rings. 3) Which of the characteristics you chose does Pluto share with each of these groups? similar to Terrestrial planets: similar to Jovian planets: not similar to either Terrestrial or Jovian planets: In 2006 a panel of Astronomers met to determine the criteria used to define a planet. The three main parameters they came up with are that the object must: - orbit the Sun - be large enough to be spherical (small objects are lumpy/potato shaped) - clear its orbit free of debris (no asteroids, no Kuiper Belt Objects, etc) 4) Given this information, is Pluto a planet? Yes No Explain. 28

31 Pluto Part 2: Comparison to Kuiper Belt Objects Kuiper Belt Objects (KBO s) orbit the Sun from 40 AU to 500 AU, are composed of rock and ice, and are generally less than 1,000 km across and so they are generally not round. 5) Is Pluto within the Kuiper Belt? 6) How does the composition of Pluto compare to KBO s? 7) What are the sizes of most KBO s compared to the size of Pluto? 8) Given this information, could Pluto be classified as a KBO? Explain. Part 3: Comparison to Dwarf Planets The panel of astronomers defined a new category of planet called dwarf planets. These objects 1) orbit the Sun, 2) are spherical in shape (roughly 1,000 km in diameter or larger), but 3) have not cleared the debris from their orbits. A photograph of Ceres is shown to the right (933 km diameter). It has an orbit at 2.8 AU from the Sun, within the asteroid belt between Mars and Jupiter. 9) Should Ceres be called a planet, an asteroid, or a dwarf planet? Explain. Ceres A photograph of Ida is shown to the right (50 km diameter). It has an orbit at 2.9 AU from the Sun, within the asteroid belt between Mars and Jupiter. 10) Should Ida be called a planet, an asteroid, or a dwarf planet? Explain. Ida A photograph of Eris is shown to the right (2,400 km diameter). It has an orbit that averages 96 AU from the Sun and is large enough to be spherical although we don t yet have clear enough images to confirm this. Eris (best image) 11) Should Eris be called a planet, an KBO, or a dwarf planet? Explain. Part 4: Making a decision 12) After thinking about all of these different characteristics of Pluto, as a committee, decide how to classify Pluto. Use the space below to explain the deciding factors that helped you make a decision. 29

32 Missions Part 1: Understanding Previous Missions Below is a condensed list of major American missions. Parentheses indicate the arrival year if different than the year sent. Flyby indicates the spacecraft did not orbit around the planet Mariner series. Flybys past Venus and Mars Apollo series; humans on the Moon 1972 Pioneer 10 to Jupiter (1973) flyby 1973 Mariner 10 to Mercury (1974) 1973 Pioneer 11 to Jupiter (1974) and Saturn (1979) flyby 1975 Viking I and II with landers to Mars (1976) 1977 Voyager I to Jupiter (1979) and Saturn (1980) flyby 1977 Voyager II to Jupiter (1979), Saturn (1981), Uranus (1986) and Neptune (1989) flyby 1978 Pioneer Venus Orbiter to Venus 1989 Galileo to Jupiter (1995) 1989 Magellan to Venus (1990) (radar altimeter) 1994 Clementine orbiter to the Moon 1996 Mars Global Surveyor orbiter to Mars (1997) 1996 Pathfinder and Sojourner rovers to Mars (1997) 1997 Cassini orbiter to Saturn (2004) (Huygens probe (lander) to Titan) 2001 Mars Odyssey orbiter to Mars 2003 Spirit rover and Opportunity rover to Mars (2004) 2003 Mars Express orbiter to Mars 2004 Messenger to Mercury (2008) 2005 Mars Reconnaissance Orbiter to Mars (2006) 2006 New Horizons to Pluto (2015) 2007 Phoenix to Mars (2008) 1) During which decade were the fewest missions sent? 1970 s 1980 s 1990 s 2) Where have we sent the most missions? (circle) Mercury Venus Mars Jupiter Saturn 3) What is one advantage of sending a rover? In what cases might an orbiter be better? The Cassini mission included a lander for its moon Titan which has an atmosphere and liquid methane. This is the first moon besides our own on which we have landed a space craft. 4) Why is NASA interested in landing on Mars and Titan when we still haven t landed on Mercury s surface? Part 2: Funding Missions 5) For each pair of proposals, state which proposal you would fund. For the proposals you do not fund, explain how to improve the proposal. Explain your reasoning in terms of a) the benefits of using an orbiter vs. lander vs. rover, b) our current knowledge about the planets, and c) funding (could you learn the same amount for less money?). Project Uno: A lander to Jupiter to understand more about volcanoes, sand dunes and how landforms are eroded by acid rain. Project Eins: An orbiter to Venus to study the atmospheric environment and greenhouse warming. 30

33 Missions Project Dos: An orbiter to Mercury to map the topography and learn more about the geology, interior structure and craters. Project Zwei: A rover to Titan to photograph the whole surface and understand the atmosphere and global environment. Project Tres: An orbiter to Uranus to learn more about Jovian storms. Project Drei: A lander to Mars to drill into the ground to look for frozen or liquid water. Project Quatro: A rover to Venus to study the formation of volcanoes. Project Vier: A lander to Europa to use seismic waves to learn about the thickness of the ice. Part 3: Proposing future missions NASA adopted a plan called Faster, Better, Cheaper in the 1990 s due to budget cuts. It began funding smaller proposals and reduced its funding for large scale proposals. Now, the missions cost about the same to send as it does to make a large-budget movie! 6) Outline your own proposal for a mission to a planet or other moon in our Solar System. Discuss whether you would send an orbiter, lander or rover as well as any instruments you would want to include. Most importantly, explain why your project should be the one that gets funded! 31